PSK enforcement on a touchback

[RyanBuckingham]

This is my first post, so please be gentle.

I'm now the R on my crew, and in hopes of staying sharp all off-season, I am sending bi-weekly quizzes to my crew. First one involves this scenario:

K has 4th and 10 from the 50 yard line. K11 punts to R1 who muffs the punt and the ball bounces into the end zone where it is recovered by K9. Before the kick ends, R2 holds K10 at R's 12 yard line.

What is the enforcement spot following the touchback? I say the PSK spot is where the kick ends (end zone), therefore the enforcement is from R's 20-yard line. Another guy on my crew says the PSK spot is from the 12-yard line since that spot is behind the 20 yard line.

Who is right? My reference is Rule 10.4.3